1. Field of the Invention
The present invention relates to downhole radiation measurement assemblies.
2. Description of the Related Art
Downhole radiation measurement assemblies have been used in drilling operations for some time. In downhole drilling it is useful identify sub-surface rock formations and customize drilling assemblies and drilling methods to suit a particular geological formation. This can be useful when, for example, a drilling rig has been configured to be effective for a particular type of rock formation and characteristics of the rock formation change as the wellbore extends deeper beneath the surface. It would thus be useful to identify rock formations present at various drilling depths at a wellsite. Downhole radiation measurement assemblies measure the naturally occurring low level radiation that is given off by rock formations downhole. Different types of rock can give off differing amounts of radiation or radiation having other differing characteristics and if measured accurately, the type of rock formations at different depths can be identified. Often, radiation measurement assemblies are deployed downhole and many measurements are taken at different depths in a well. The sensor measurements can then be communicated uphole and processed to determine the particular types of rock formations present at various depths at a particular wellsite. Radiation measurement assemblies can experience harsh vibrations and temperatures as well as other environmental conditions during the installation process, when taking radiation measurements, while sitting downhole, and also during retrieval. Over time drilling operations have seen drilling to greater depths, causing radiation measurement assemblies to experience increasingly harsher environments. In addition, many of the radiation measurement sensors can be particularly sensitive and malfunction in response to vibration, harsh temperatures, and other environmental factors. Vibration factors can be particularly problematic for radiation measurement sensors used in downhole radiation measurement assemblies. This can be due in part to the construction and sensitive components of radiation measurement assemblies. These factors and others continue to create the need for more advanced and reliable downhole radiation measurement assemblies.
Radiation measurement assemblies are commonly deployed with measurement while drilling tools. The purpose of measurement while drilling tools is to collect various sensor based measurements and facilitate the communication of the measurements to the surface. Measurement while drilling tools can be deployed with sensors for measuring various downhole conditions such as temperature, flow data, drillstring rotation, location information, radiation readings, or other useful downhole conditions. The sensors deployed alongside or as a part of measurement while drilling tools will often be configured to communicate data with the microcontroller or microprocessor that is a part of the measurement while drilling tool assembly deployed downhole. This communication may be made using standard protocols that transmit over bus connections between the measurement while drilling tool and the various sensors. Measurement while drilling tools can then communicate data from the sensors uphole to remote computers or data logging equipment. Measurement while drilling tools can be deployed by wireline or inline with the drillstring and can include remote power supplies or receive power over cabling run downhole. It is common to deploy a radiation probe that is connected to a measurement while drilling tool downhole to perform radiation measurements at various depths. The measurement while drilling tool can be configured to receive gamma probe data, which for example may be in the form of a pulse train, and then process and communicate the data to remote computers on the surface.
It would be desirable to have radiation measurement assemblies that include greater resilience to vibration, harsh temperatures, and other environmental factors that are present downhole. Further, it would be desirable to provide increased meantime between failures of radiation measurement assemblies installed downhole. This would allow greater drilling time, increased measurement time, and decreased time spent installing, retrieving, and servicing radiation measurement assemblies. It would further be desirable to decrease the time committed to servicing radiation measurement assemblies due to the failures of radiation measurement sensors that are particularly sensitive to the harsh environments downhole.